Sensors and sensor modules worn on the body to measure or monitor biosignals, such as for example electrocardiogram (ECG), electroencephalogram (EEG), electromyogram (EMG), bioimpedance or photoplethysmogram (PPG) signals, frequently suffer from artifacts caused by motion of the body, especially when the sensors are intended to operate in continuous or ambulatory mode. A key technical challenge in such application environments is overcoming motion artifacts that significantly affect the measurements when the body is moving.
Patent application EP 2 792 297 A1, for example, describes a system for the analysis of biopotential signals, comprising a motion classification module configured for determining motion information comprising the type and/or severity of the motion phenomena causing artifacts in the biopotential signal and communicating the motion information to a motion artifact reduction module, which will perform motion artifact removal from the biopotential signal based on the information received from the motion classification module. The motion classification module receives one or more secondary inputs related to the subject or electrode motion and/or direct or indirect artifact distortion, where the secondary inputs being, for example, electrode-to-tissue impedance, applied or contact force or acceleration of/on the electrode.
U.S. Pat. No. 5,513,649 also describes a system to detect brain waves from a subject, wherein the adverse effect on the EEG recording of artifacts due to head, body and eye movements is reduced. A reference signal of the movement contaminating the EEG signals is provided by one or more of several alternatives, including an accelerometer or other type of motion detector, and spatial averages of the EEG channels. For example, an accelerometer or a motion detector detects head motion and determines the starting and ending of movement artifact and the spatial average EEG signal is the reference signal which is used only during such movement artifact. An adaptive digital filter removes the contaminants caused by the head, body and eye movements to produce corrected and usable EEG signals.
Also, U.S. Patent Application No. 2008/0208028 and U.S. Patent Application No. 2012/0143020 describe systems for the analysis of biopotential signals in which further motion artifact reduction or motion artifact handling techniques are used.
There is a motivation to improve current systems for the analysis of biosignals in order to obtain better motion artifact reduction.